The present invention relates to a continuous method for making polyetherimide, based on the introduction of molten aromatic bis(ether anhydride) and molten organic diamine into an extruder reactor.
Prior to the present invention, as shown in Takekoshi et al, U.S. Pat. No. 4,011,198, incorporated herein by reference and assigned to the same assignee as the present invention, there is provided a method for making polyetherimides by effecting reaction at melt polymerization temperatures between an aromatic bis(ether anhydride), or "organic dianhydride" and an organic diamine in an extruder. The organic dianhydride has the formula, ##STR1## and the organic diamine has the formula, EQU H.sub.2 N--R.sup.1 --NH.sub.2, (2)
where R is a member selected from ##STR2## and divalent organic radicals of the general formula, ##STR3## X is a member selected from the class consisting of divalent radicals of the formula, ##STR4## y is an integer from 1 to 5; and R.sup.1 is a divalent organic radical selected from the class consisting of aromatic hydrocarbon radicals having from 6 to about 20 carbon atoms and halogenated derivatives thereof, alkylene radicals having from 2 to about 20 carbon atoms, cycloalkylene radicals having from 3 to about 20 carbon atoms, from C.sub.2 to about C.sub.8 alkylene terminated polydiorganosiloxanes and divalent radicals of the general formula, ##STR5## Q is a member selected from the class consisting of EQU --O--, --S--, C.sub.x H.sub.2 x,
x is an integer from 1 to 5 and n is 0 or 1.
Further improvements in the melt polymerization of mixtures of organic dianhydride of formula (1) and organic diamine of formula (2) to make polyetherimide are shown by Banucci et al U.S. Pat. No. 4,073,773, incorporated herein by reference and assigned to the same assignee as the present invention. Banucci et al show the introduction of a powdered mixture of organic diamine and aromatic bis(ether anhydride) into an inlet opening of a screw extruder. The powdered mixture of organic diamine and aromatic bis(ether anhydride) were blended in certain proportions and attempts were made to maintain the powdered mixture as uniform as possible. The preformed powdered blend was passed through a first extruder zone maintained at a low temperature to a zone where the mixture was melted and water of reaction was removed.
Although the methods of Takekoshi et al and Banucci et al provide procedures for making polyetherimide in an extruder by melt polymerization of a mixture of organic dianhydride of formula (1) and organic diamine of formula (2), steady state conditions required for continuous production of polyetherimide by melt polymerization are often difficult to achieve. The temperature profile of monomer solids initially introduced into the extruder have to be carefully monitored prior to the venting of water of reaction to avoid plugging of the monomer feed in the extruder. The conversion of the solid monomers to the molten state can occur in Banucci et al at the mass transfer stage where water is evacuated. This procedure can interfere with the creation of steady state conditions in the extruder and optimum polymerization conditions for making polyetherimide.
The present invention is based on the discovery that steady state conditions suitable for polyetherimide formation in a continuous manner can be achieved by separately introducing into a screw extruder organic dianhydride of formula (1) and organic diamine of formula (2) in the liquid state in particular proportions, thereafter further kneading the aforementioned ingredients in the molten state prior to conveying the resulting liquid to a mass transfer stage to effect the separation of water of reaction.
It has been found that optimum results can be achieved with respect to the introduction of liquid organic dianhydride of formula (1) and organic diamine of formula (2) by employing a concentric feed pipe as shown in FIG. 2 and copending application Ser. No. 459,851 to allow for the controlled metering of organic dianhydride and organic diamine. Surprisingly, initial contact between the molten organic diamine at temperatures in the range of from 200.degree. C. to 275.degree. C. at pressures of up to about 2 atmospheres, does not result in reaction by-products based on the instantaneous intercondensation between the organic diamine and the organic dianhydride, which would impede forward material flow and impair ultimate polymer properties. A two-phase liquid mixture is formed which can be kneaded and conveyed to a mixing stage at even higher temperatures and pressures without substantially affecting ultimate polymer properties prior to the evacuation of water of reaction. As shown hereinafter, particular proportions between the organic dianhydride and the organic diamine, and certain blending conditions the organic dianhydride and organic diamine can provide polyetherimide having optimum properties.